The Circulation - Chapter 6

Question 1

What percentage of total blood volume is in veins?

Answer 1

67% ish

Question 2

Where in circulation does the smallest diameter and therefore largest pressure drop occur?

Answer 2

In arterioles

Question 3

What does Poiseuille’s equation demonstrate?

Answer 3

Mean flow depends on vascular resistance?

Question 4

What are the two types of capillaries?

Answer 4

True capillaries and A-V capillaries (have muscle coat and sphincter to control flow)

Question 5

How do diameters of capillaries compare to RBCs?

Answer 5

They are smaller and so distort the RBCs

Question 6

What drives net movement of fluid across capillaries?

Answer 6

Starling’s forces - osmotic and hydrostatic pressure

Question 7

What does tissue perfusion depend on?

Answer 7

The A-V pressure difference
BP = CO x TPR

Question 8

What happens to hydrostatic pressure when you move from supine to standing?

Answer 8

Hydrostatic pressure becomes negative for all arteries above the heart and positive below the heart

Question 9

When standing, what are approximate differences in hydrostatic pressure at the head and the feet?

Answer 9

Head - hydrostatic pressure: -40mmHg
Feet - hydrostatic pressure: 100mmHg

Question 10

What is the impact of the increased hydrostatic pressure below the heart on the veins?

Answer 10

It causes increased venous volume due to compliance

Question 11

What happens to the aorta as we age?

Answer 11

Mechanical fatigue of elastin causes increased aortic diameter
The wall becomes stiffer

• This causes an increase in pulse wave velocity
• the increase in elastic modulus outweighs the increase in radius

Question 12

What governs / changes the carotid artery waveforms as we age?

Answer 12

Waveforms depend on the reflected waves from peripheral sites i.e. the aortic bifurcation, and the elasticity of the arteries

Question 13

What happens to aortic pulse wave velocity as we age?

Answer 13

The pulse velocity increases due to the decrease in elasticity of the vessel walls
- Pulse wave velocity more than doubles as we age
- this causes loss of low frequency harmonics = less cardiac efficiency

Question 14

What happens to the location/timing of the aortic bifurcation reflection on the carotid waveform as we age?

Answer 14

Aortic pulse wave velocity increases
The reflection moves from early diastole towards systole

Question 15

What causes the dicrotic notch?

Answer 15

Aortic valve closure

Question 16

What happens to characteristic impedance as we age?

Answer 16

It increases
- there is an increase in pressure in late systole due to the reflected wave arriving back at the heart before ejection is finished